What is the value of d sub 21 plus d sub 22 plus d sub 23 given the matrix equation? cap d plus the 3 by 3 matrix, row 1, column 1, 1 column 2, 0 column 3, 1 row 2, column 1, negative 3 column 2, 9 column 3, negative 7 row 3, column 1, negative 20 column 2, 2 column 3, 4 is equal to the 3 by 3 matrix, row 1, column 1, 9 column 2, negative 3 column 3, 2 row 2, column 1, 8 column 2, negative 1 column 3, 0 row 3, column 1, 11 column 2, 15 column 3, 3